1. Field of the Invention
The invention is directed to a vertical strip accumulator or strip storage device for bridging interruptions in a continuous strip production, such as, for example, a continuous annealing. The vertical strip storage device comprises a supporting frame which forms a looping tower. The continuous strip is looped around deflecting rollers at upper and lower horizontal roller bridges in the looping tower which are synchronously vertically movable, one above the other, toward and away from one another. The inherent weight of one roller bridge compensates for the inherent weight of the other roller bridge as a counterweight. One roller bridge is always at the upward cable portion of a vertically deflected joint cable drive and the other roller bridge is always at the downward cable portion of this vertically deflected joint cable drive. The joint cable drive includes rollers supported in the upper region and in the lower region of the supporting frame.
2. Description of the Related Art
Vertical strip storage devices of the above-described type are known as loop towers or loopers and are employed in continuous strip production for maintaining continuous process speed during coil handling, such as when changing coils and/or welding the start of the coil to the end of the strip. Long lengths of strip can be stored temporarily in these vertical strip storage devices in that enlarged loops of the strip are guided alternately around upper and lower deflecting rollers of roller bridges. The enlarging of the loops is effected, for example, by moving the upper roller bridge upward in the supporting frame while the lower roller bridge remains stationary, so that the length of strip stored between the roller bridges increases. To move the extremely heavy roller bridge upward, it is known to arrange counterbalances or counterweights laterally outside of the supporting frame. The counterweights are connected with the movable roller bridge by coupling cables or chains via deflecting rollers and compensate for the inherent weight of the movable roller bridge.
However, the known construction has disadvantages including the extreme elaborateness and high cost of materials required for compensating the weight of the movable roller bridge and the very time-consuming and labor-intensive threading of the strip after a breakage of strip, which is inevitable from time to time in such prior art devices. For at least these reasons, an improved vertical strip storage device was proposed in reference DE-U-295 21 303. In the improved strip storage device, both the upper and lower roller bridges are movably guided, one above the other, in the supporting frame so as to be synchronously movable toward and away from each other. In this improved configuration, the inherent weight of one of the roller bridges acts as a counterbalance to compensate for the inherent weight of the other of the roller bridges.
In contrast to previous solutions, rather than moving either the upper roller bridge or the lower roller bridge in the supporting frame, both roller bridges are now guided so as to be synchronously movable, such that the inherent weights of the roller bridges offset one another. This eliminates the considerable cost for counterweight compensation which was required in the prior known solution, which represents savings in the production of the overall plant, even considering the cost of the second movable roller bridge. Moreover, the suggested solution achieves a further advantage in that the roller bridges are moved apart and are moved together at half-speed to effect the same result as the prior known solution because one roller bridge is at the upward portion of vertically deflected cable drives or chain drives which are driven jointly at the same speed and the other roller bridge is at the downward portion of these drives. A halving of the driving speed such as this also enables more economical gearing configurations.
Despite the cost advantages of this improved strip storage device, the drive and cables for moving the roller bridges remain large and costly.